The present subject matter relates generally to the field of microbiology and immunology. In particular, the present subject matter relates to immunogenic compositions useful for inducing an immune response that may serve to protect an animal from infection by a pathogen. Reference is made herein to Okwumabua et al., CLIN DIAGN LAB. IMMUNOL. 2005, 12:484-490. All patents and publications cited herein are hereby incorporated herein by reference.
Microorganisms such as Streptococcus species are important swine pathogens. For example, Streptococcus suis causes many pathological conditions, such as arthritis, endocarditis, meningitis, polyserositis, and bronchopneumonia. Streptococcus suis also is an important zoonotic agent for people in contact with swine or their by-products and causes meningitis, permanent hearing loss, and septic shock. Thirty-five capsular types (types 1/2 and 1 to 34) are currently known. Type 2 is considered the type that is the most frequently associated with disease and is the type that is the most often isolated. Strains of other serotypes, such as serotypes 1/2, 7, 9, and 14, can also cause disease. Attempts to control the infection are hindered by a lack of thorough knowledge of the virulence factors and protective antigens of the bacterium, the existence of multiple serotypes with diverse genetic makeups, and the evolution of multidrug-resistant strains.
Several protein components, including attenuated whole bacterial cells, have been evaluated as vaccines against S. suis. However, these studies did not achieve much success because the protection was either serotype or strain dependent, and in some instances the results were ambiguous. For example, Jacobs et al., (VET. REC. 139:225-228 (1996)), evaluated a suilysin-based subunit vaccine and showed that it conferred complete protection. However, the absence of suilysin in a substantial number of isolates recovered from diseased pigs hampers the use of this vaccine. Thus, identification of other antigenic factors will contribute to the development of a monovalent or a multivalent subunit vaccine that will protect pigs against infection by all capsular types.
In our effort to identify an S. suis gene(s) that may be involved in virulence and proteins that may be useful in the development of a reliable diagnostic reagent or vaccine to protect against infection with this bacterium, we identified a DNA region from a virulent strain of S. suis serotype 2 that encoded a polypeptide of 38 kDa. Of the 35 S. suis serotypes currently known, 31 contain and express the gene. The gene product was reactive with serum from pigs with S. suis infection, and the protein induced protective immunity in experimentally challenged pigs, making it a candidate for consideration in the development of a diagnostic reagent and vaccine.